This invention relates to a method and burner for igniting a fragmented permeable mass of formation particles containing oil shale within an in situ oil shale retort in a subterranean formation containing oil shale.
The presence of large deposits of oil shale in the Rocky Mountain region of the United States has given rise to extensive efforts to develop methods for recovering shale oil from kerogen in the oil shale deposits. It should be noted that the term "oil shale" as used in the industry is, in fact, a misnomer. It is neither shale nor does it contain oil. It is a sedimentary formation comprising marlstone deposit with layers containing an organic polymer called "kerogen" which, upon heating, decomposes to produce liquid and gaseous products. It is the formation containing kerogen that is called "oil shale" herein and the liquid hydrocarbon product is called "shale oil".
A number of methods have been proposed for processing oil shale which involve either first mining the kerogen bearing shale and processing the shale on the ground surface or processing the oil shale in situ. The latter approach is preferable from the standpoint of environmental impact since the treated shale remains in place reducing the chance of surface contamination and the requirement for disposal of solid wastes.
The recovery of liquid and gaseous products form oil shale deposits has been described in several patents such as U.S. Pat. Nos. 3,661,423; 4,043,595; 4,043,596; 4,043,597; 4,043,598; 4,118,071; and 4,153,298, as well as pending applications including U.S. Patent Application Ser. No. 929,250 filed July 31, 1978, by Thomas E. Ricketts, now U.S. Pat. No. 4,192,554. Each of these patents and the application is assigned to Occidental Oil Shale, Inc., assignee of this application and each is incorporated herein by this reference.
These patents describe in situ recovery of liquid and gaseous hydrocarbon materials from a subterranean formation containing oil shale wherein such formation is explosively expanded towards one or more excavated voids to form a stationary fragmented permeable mass of formation particles containing oil shale within the formation, referred to herein as an in situ oil shale retort or merely as a retort.
Retorting gases are passed through the fragmented mass to convert kerogen contained in the oil shale to liquid and gaseous products. One method for supplying hot retorting gases used for retorting kerogen contained in the oil shale, as described in the aforementioned patents, includes establishing a combustion zone in an upper portion of the retort and introducing an oxygen supplying retort inlet mixture into the retort to advance the combustion zone downwardly through the fragmented mass. In the combustion zone oxygen from the retort inlet mixture is depleted by reaction with hot carbonaceous materials to produce heated combustion gas and combusted oil shale. By the continued introduction of the retort inlet mixture into the fragmented mass, the combustion zone is advanced through the fragmented mass in the retort.
The combustion gas and the portion of the retort inlet mixture that does not take part in the combustion process pass downwardly through the fragmented mass on the advancing side of the combustion zone to heat the oil shale in a retorting zone to a temperature sufficient to produce kerogen decomposition called "retorting". Such decomposition of the oil shale produces gaseous and liquid products including shale oil and a residual carbonaceous material.
The liquid products and the gaseous products are cooled by the cooler oil shale fragments in the retort on the advancing side of the retorting zone. The liquid hydrocarbon products, together with water produced in or added to the retort, collect at the bottom of the retort and are withdrawn. An off gas is also withdrawn from the bottom of the retort. Such off gas can include carbon dioxide generated in the combustion zone, gaseous products produced in the retorting zone, carbon dioxide from carbonate decomposition, and any gaseous retort inlet mixture that does not take part in the combustion process.
Establishment of a combustion zone in the fragmented mass involves heating a portion of the fragmented mass adjacent its upper surface to an ignition temperature so that carbonaceous material in oil shale is burned to supply heat for retorting. Ignition requires a substantial amount of heat delivered over a sufficient time to raise the temperature of particles containing oil shale above an ignition temperature. In a large retort several burners may be needed at the same time for igniting the top of a fragmented mass at several locations to assure uniformity in the combustion zone. It is therefore desirable to provide an inexpensive and reliable burner for igniting an in situ oil shale retort from a remote location.
It has been found upon forming a retort generally in accordance with the description in U.S. Patent Application Ser. No. 929,250, now U.S. Pat. No. 4,192,554, that the fragmented mass of particles in the retort did not completely fill the retort cavity. That is, a void space remained between the upper surface of the fragmented mass and overlying unfragmented formation.
When a void space exists over the top of a fragmented mass in the retort it can be desirable to place a burner in the void space for heating an upper portion of the fragmented mass with limited heating of the overlying unfragmented formation. It is desirable to impinge heated ignition gas on the fragmented mass and minimize radiant heating of overlying formation. A burner is desirable for use in a void space over a fragmented mass which operates essentially independently of the height of such a void space.
This invention is related to the invention disclosed in U.S. Patent Application Ser. No. 47,715, filed June 12, 1979, entitled APPARATUS AND METHOD FOR IGNITING AN IN SITU OIL SHALE RETORT, now U.S. Pat. No. 4,245,701, which is a continuation of U.S. Patent Application Ser. No. 953,477, filed Oct. 23, 1978, by Carlon C. Chambers and now abandoned. These patent applications are incorporated herein by this reference.